Size-resolved comprehensive characterization of airborne particulate matter

Abstract

An update of a methodology to extract both the size-segregated source apportionment of atmospheric aerosol and the size distribution of each detected element or compound, is presented. The approach is based on the parallel use of standard low-volume samplers to collect particulate matter (PM) and of an Optical Particle Counter (OPC). The methodology was introduced and validated in previous works for the average size distribution of elemental components of PM: it has now been extended to PM compounds such as ions and carbonaceous aerosol (namely, organic end elemental carbon, OC and EC). Furthermore, the methodology has been now adopted in the frame of a field campaign, proving that it is able to provide not only an average size distribution but also information on the time evolution of the size distribution of specific PM species. Samples were collected in the urban area of Genoa (Italy) and their composition was measured by Energy Dispersive X-ray Fluorescence (ED-XRF), Ion Chromatography (IC) and Thermo-optical analysis. Positive Matrix Factorization (PMF) was applied to time series of daily concentration values in PM10 and PM2.5 (i.e. fraction of PM mass with aerodynamic diameter lower that 10 μm and 2.5 μm, respectively) to identify major PM sources, and both PM mass concentration and size-segregated particle number concentration were apportioned. Seven and six sources were respectively resolved in PM10 and PM2.5, with processes related to secondary aerosol formation accounting for about 53% and 57% of PM levels in the two fractions. The new methodology is complementary to size-segregated PM sampling, and it was actually tested against a 13-stage nanoMOUDI cascade impactor. Size distributions obtained with the new methodology and directly measured by the nanoMOUDI turned out to be in good agreement (R2 > 0.60) with discrepancies observed for SO42− only.